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Under Slab Hydrostatic Testing

Step 1
The first step in an under slab hydrostatic testing process is called the overall test. An overall test is a basic general analysis of the system. At least one first floor toilet must be removed from the floor as this allows for a place to monitor and access the drain system. The drain line is blocked with an inflatable ball, filled with water and monitored for results:

(a) If the water level drops within 20 minutes then leakage is present, or
(b) If the water level maintains for 20 minutes then no leakage is present,
(c) Any and all toilets removed are reset with new seals.

In order to properly perform the test the ball must be placed in the pipe at a point immediately outside the house, this allows for the entire under slab portion of that system to be tested. A clean out is the preferred place to test from since they are usually placed close to the house and allow for access into the pipe. Not all clean outs are suitable for testing however. Videotape can be made but must be requested and are an additional cost to the testing costs.

Step 2
The second step is taken only if leakage is present and it is referred to as the isolation test. The isolation test is the process taken to determine the location of any leaks. This is a process of elimination. Any and all first floor toilets must be removed from the floor allowing for multiple test points. The inflatable ball is placed throughout the system to determine if that section is leaking. Often more than one ball is used. As in step 1 the use of a clean out is important as this allows for several areas to be tested and isolated. All toilets removed are reset with new seals.

Once isolation testing is done a map of the house indicating the line locations and leak locations is drawn up and then a repair proposal is written based on the results of the test. Repairs vary from repairing the leaks found to total under slab system replacement.

A note on Cameras
Cameras do not perform tests. While cameras allow plumbers to view the pipe and can reveal obvious breaks in the system they are not capable of reaching all sections of the system. By using water, which seeks its own level, we are able to reach all points of the system (except for areas that may be clogged). This method is not only preferred due to the higher success rate but it is the only recognized way to test when a dispute arises. Systems that are checked only with a camera are not recognized as having been “tested.” Do not be misled by companies performing “camera” tests. Of course a video can be made of the system upon request.

The steps listed above allow for the proper diagnosis of the under slab drain system and must be performed as stated or risk an incomplete, under or over stated diagnosis.

While simple enough in theory many factors determine the amount of work required to perform and complete testing. For example many houses built prior to the 1970’s have multiple systems under the house. This simply means that sections of the plumbing drain system do not join together under the house but rather exit from the house and join together in the yard. On homes with multiple systems multiple tests are required since the testing must only be performed on the under slab sections. Testing the yard portions can and often do results in leaks being recorded as the yard lines are usually not always water tight. In these cases clean outs should be installed to properly record the under slab results. Where clean outs are not available or not easily installed cameras may be used to help place the test ball in the line at a point just outside the home. While this scenario will allow for a test it can lead to a false conclusion that a leak is present as there is no place to view wherever or not water is escaping past the ball. Clean outs are important and they also allow for a more thorough isolation of any leaks. (click the following link to view under slab plumbing diagrams)

Another factor is the overall size and length of the system. Large spread out homes often have long lengths of piping under them and depending on the number and location of leaks present this can lead to large sections of pipe going untested. Other factors that may hinder testing include type and size of pipe, heavily corroded pipes, numerous leaks, blockages, lack of proper or accessible vents, multiple turns in the system, overall length of the system, exit lines located under concrete or decking, just to name a few.

While this summary should answer most questions, once the plumber is on site, has surveyed the home and has begun step one he can better determine the situation and report what he is challenged with. Pricing based on the specific situation can then be given in order to proceed beyond the basic overall test. Click the following link for more information about When to do under slab drain testing.

Misinformation about testing and the process often confuses the situation, this summary should help in the understanding of how testing is done on the professional level. Licensed professional plumbers possess the understanding of how a drain system works which allows them to properly diagnose problems and to properly draw up a repair plan. A licensed plumber will always notify and consult when obstacles are encountered.


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